Such filters are known at the present time, for example called "Greenfield filters" or "Mobin-Uddin filters" (U.S. Pat. No. 3,540,431), constituted by filiform elements disposed so as to constitute a cone permeable to the blood flow.
In order to fix the filter in the vein, the ends of the filiform elements constituting the filtration means are generally provided with hooks for anchoring, hooking in the inner wall of the vein, as described in U.S. Pat. No. 4,425,908, FR.A. No. 2 587 901 and EP.A. No. 0 270 432.
In order to implant such filters, the endovenous route is generally used; more precisely, the filter is introduced through a small vein, such as the jugular vein or the femoral vein, then the filter is guided and led towards the inferior vena cava, where it will be fixed in stable manner on opening out.
To facilitate passage, a catheter is used which, depending on the dimensions, is introduced during a surgical operation or by carrying out a method of percutaneous introduction which is less aggressive for the patient. This being so, the great majority of the existing filters are "definitive", i.e. once implanted, they can no longer be removed from the patient.
In fact, the structure of these filters is such that the means for fixing the filter, formed by anchoring hooks, hook in the inner wall of the vein, which prohibits any reverse passage.
However, certain patients present a risk of pulmonary embolism only during a brief period of time. In fact, for example, during a period of operation, or when the patients have peripheral clots, said clots may be dissolved rapidly by fibrinolytic drugs, which does not justify the definitive insertion of a clot filter.
This is why it is of interest to have available filters for the vena cava, adapted to be positioned temporarily, i.e. adapted to be left in place only for some days, for example.
In fact, in such cases, from the clinical standpoint, two possibilities exist, namely: dissolution and complete disappearance of the clots, or aggravation of the risk and persistence of the clots.
Concerning the filters for temporary use, filters similar to the definitive filters are used at the present time, although they do not bear anchoring hooks in order to allow them to be withdrawn in reverse by the endovenous route. FR. No. A.2 580 504 describes a temporary filter of this type.
In order to fix the known temporary filters, i.e. in order to avoid migration thereof in the vein, a guide is generally used, on the one hand fixed to the temporary filter and which, on the other hand, passes in the blood vessel up to the point of puncture where it is maintained in place for example by stitches.
If the evolution is satisfactory, i.e. when radiographic checks show that the state of the veins and of the vena cava has become normal and the risks of embolism have disappeared, it is advantageous to be able to remove the filter.
On the other hand, if the situation remains preoccupying and the risk of embolism remains great, it is necessary to maintain the filter in place.
Now, if a temporary filter has been used, it is then necessary to replace it by a definitive filter, which involves re-operating, either by carrying out a new operation to position another filter, or by replacing the temporary filter in place by a new definitive filter, making it necessary to reintroduce catheters and metal guides at the zone of puncture, which presents a considerable risk from the standpoint of infectious contamination.
The uncertain evolution from the clinical standpoint and the mastery of the risks of embolism being delicate, it would be of interest to have available a temporary and/or definitive filter which, after some days, may be withdrawn or be left in place definitively, without it being necessary to introduce catheters or metal guides into the patient's venous system again.
It is an object of the present invention to propose such a filter for medical use, particularly intended to be implanted in a vessel, such as the inferior vena cava, by the endovenous route, via a catheter, which overcomes the drawbacks of the known filters.
In other words, one of the objects of the present invention is to propose a filter for medical use, for temporary and/or definitive use, which may either be withdrawn without detriment to the patient's venous system, or be left definitively in place, avoiding a fresh operation which would be detrimental, taking into account the risks of infectious contamination.
Another object of the present invention is to propose a filter for medical use, adapted to be implanted by the endovenous route in the vena cava, whose definitive fixing is reinforced in order to avoid the migration of the filter during peristaltic movements.
A further object of the present invention is to propose a catheter designed for positioning and using the filter of the invention, which in particular, allows implantation thereof by the percutaneous endovenous route.
Yet another object of the present invention is to propose a catheter which controls and maintains said filter in temporary use.
In addition, said catheter of the present invention allows the introduction, upstream of the filter, of fibrinolytic product to lyse the clots which may be formed or be trapped in the filter, and in order to be able, thanks to the injection of constrast media, to check the existence of clots at the level of the filtering zone.
It is a further object of the present invention to propose a catheter which makes it possible either to withdraw the filter very easily, or to leave it in place definitively without it being necessary to re-operate.
Another object of the present invention is to propose a catheter of this type whose operation is perfectly reliable despite the risk of accumulation of fibrin.
Yet another object of the present invention is to propose a filter intended to be implanted in a vessel which, in definitive or temporary position, performs a good function of filtration, non-aggressive for the inner walls of the vessel.
Other objects and advantages of the present invention will appear in the course of the following description which has, however, only been given by way of indication and is in no way limiting.
According to the present invention, the filter for medical use, particularly intended to be implanted in a vessel such as the inferior vena cava, by the endovenous route via a catheter, said filter comprising filtering means adapted to open out in said vessel when it is positioned in the patient, is characterized in that the filtering means present no means for hooking on the wall of the vein and in that it comprises means for holding the filtering means in place with respect to the vessel, adapted to allow the passage from a situation of temporary use, i.e. being maintained for a certain period of time, the filter may be withdrawn without damage to the vessel, to a situation of definitive use, i.e. the filter may be left in place, solidly fixed on the wall of the vessel.
In addition, the catheter designed for positioning and using the filter of the invention, presenting a proximal end and a distal end, said filter, prior to being implanted in the patient, being placed at the distal end of the catheter, is characterized in that it comprises:
a down-sheath of which the distal end is adapted on the one hand to h o 1 d the filtering means non-opened out during introduction of the filter and, on the other hand, fixedly to contain the holding means during the introduction of the filter, its temporary use and its withdrawal after temporary use,
a pusher, manoeuvrable from the proximal end of the catheter, adapted, for definitive use of the filter, to expel said holding means out of the down-sheath at its distal end.
It will be readily appreciated that, contrarily to what is taught in the Patents mentioned hereinabove which describe definitive filters, the filtering means must imperatively be bereft of means for hooking on the vein wall, so that, in the event of withdrawal of the filter, the filtering means may slide inside the vein without damaging it.